A steering device for a motor vehicle is configured as shown in FIG. 33 in which rotation of a steering wheel 1 is transmitted to an input shaft 3 of a steering gear unit 2, and a pair of left-right tie rods 4 are pushed and pulled in response to the rotation of this input shaft 3, thereby giving a steering angle to front wheels. The steering wheel 1 is supported and fixed on a rear end section of a steering shaft 5, and this steering shaft 5 in a state of being inserted in the axial direction of a cylindrical steering column 6, is rotatably supported on this steering column 6. Moreover, a front end section of the steering shaft 5 is connected, via a universal joint 7, to a rear end section of an intermediate shaft 8, and a front end section of this intermediate shaft 8 is connected, via another universal joint 9, to the input shaft 3.
Heretofore, there have been known, in this type of steering device, a tilt mechanism for adjusting the up/down position and a telescopic mechanism for adjusting the front/rear position of the steering wheel 1 according to the physique and driving posture of the driver.
In order to configure the tilt mechanism capable of up/down direction displacement, the steering column 6 is supported so as to be capable of swing displacement about a pivot shaft 11 which is installed in the widthwise direction on a vehicle body 10. Moreover, a displacement bracket fixed on a portion closer to the rear end of the steering column 6, is supported so as to be capable of displacement in the up/down and front/rear direction with respect to a support bracket 12 supported on the vehicle body 10. The widthwise direction here refers to the widthwise direction of the vehicle body, corresponding to the left-right direction, and the front/rear direction refers to the front/rear direction of the vehicle body.
Furthermore, in order to configure the telescopic mechanism capable of front/rear direction displacement, the steering column 6 is of a structure which telescopically combines an outer column 13 and an inner column 14, and the steering shaft 5 is of a structure which combines an outer shaft 15 and an inner shaft 16 in spline engagement, allowing free torque transmission and free telescopic motion. In the example shown in the diagram, there is also incorporated an electrically-operated power steering device which reduces the amount of force required for operating the steering wheel 1, using an electric motor 17 as an auxiliary power source.
In the case of the tilt mechanism and telescopic mechanism, excluding those of an electric type, the position of the steering wheel 1 is brought to an adjustable state or it can be fixed at a post-adjustment position, based on the operation of an adjustment lever. For example, Patent Document 1 discloses a structure shown in FIG. 34 and FIG. 35 in which the axial dimension of a cam device 20 is expanded and contracted and a cam member 21 is swing-displaced at the same time, based on rotation of a rod-shaped member 19 based on an adjustment lever 18. In the case of this conventional structure, based on expansion and contraction of the cam device 20, a movable side bracket 22 fixed on an outer column 13a is engaged with and disengaged from a support bracket 12a. Moreover, whether or not an inner column 14a is allowed to slide with respect to an outer column 13a is switched based on swing displacement of the cam member 21.
In the case of this type of conventional structure disclosed in Patent Document 1, compared to structures therebefore (prior structures), the number of friction engagement sections in fixing the front/rear position of the steering wheel 1 is increased to thereby increase the level of strength and rigidity associated with this front/rear position fixation. However, there is room for improvement in order to further enhance driver protection by not letting the position of the steering wheel 1 change regardless of a large impact load applied to the steering wheel 1 in the event of a collision accident. This point is described below.
In the event of a collision accident, following a so-called primary collision in which a motor vehicle collides with another motor vehicle, there occurs a so-called secondary collision in which the driver's body collides with the steering wheel 1. When this secondary collision occurs, a large diagonally forward-upward impact load is applied to the steering wheel 1. On the other hand, in the case of the conventional structure shown in FIG. 34 and FIG. 35, the force which fixes this steering wheel 1 at a post-adjustment position is obtained only by frictional force, and therefore, there is a possibility that this position may be displaced based on a large impact load. Specifically, there is a possibility that the position of the steering wheel 1 may be displaced forward or upward. As a result of this, the positional relationship between this steering wheel 1 and the driver's body is displaced from the post-adjustment position, which is an optimum position. In this state, an airbag expanded and deployed in the rear of the steering wheel 1 becomes unable to effectively catch the driver's body, and it serves adversely in terms of driver protection.
As a structure for preventing displacement of a steering wheel at the time of a secondary collision, heretofore, there are known structures disclosed in Patent Documents 2 and 3. In the case of the conventional structure disclosed in Patent Document 2, a pair of retention arms are arranged on both sides of a plate piece fixed on the outer circumferential surface of a steering column, and at the time of a secondary collision, this plate piece is firmly clamped by both of these retention arms to prevent forward displacement of the steering column. In this type of conventional structure disclosed in Patent Document 2, unless the accuracy of each constituent is sufficiently ensured, there is a possibility that the force for preventing forward displacement of the steering column may become uneven, consequently making this displacement prevention unreliable. Furthermore, in a structure which prevents forward displacement (in the telescopic direction), upward displacement (in the tilt direction) cannot be prevented.
Moreover, Patent Document 3 discloses a structure as shown in FIG. 36 in which an eccentric cam 23 is provided on a movable side bracket 22a fixed on a steering column 6a, and in a case where this steering column 6a tends to be displaced upward, a serrated section 24 provided on the outer periphery of this eccentric cam 23 is interlocked with the rear end edge of a support bracket 12b provided on the vehicle body side, to thereby prevent upward displacement of the steering column 6a. This type of conventional structure disclosed in Patent Document 3 has a superior function of preventing this upward displacement, however, it does not have a function of preventing forward displacement. An application of the structure disclosed in Patent Document 3 to a structure which prevents forward displacement of an inner column may be considered. However, if the application is made with no change, there is a possibility that a smooth adjustment of the front/rear position of the steering wheel may not be possible in normal operation.
That is to say, in order to perform a smooth adjustment of the front/rear position of the steering wheel without creating excessive resistance and abnormal noise, the serrated section of the eccentric cam and the outer circumferential surface of the inner column need to be reliably separated from each other in a state where an adjustment lever has been turned to a lower position for this front/rear position adjustment. On the other hand, in recent years, it has been considered that respective constituent members for position adjustment of a steering wheel are to be installed above a steering column in order to minimize the size of a portion which projects downward from the steering column for protecting the knee part of the driver in the event of a collision accident. If, with this type of structure, the forward prevention structure for the inner column with the eccentric cam described above is practiced, even in a state where the adjustment lever has been turned to adjust the front/rear position of the steering wheel, the eccentric cam is turned downward by its own weight, and the serrated section of this eccentric cam and the outer circumferential surface of the inner column are likely to stay in contact with each other. In this type of state, an up/down position adjustment of the steering wheel cannot be smoothly performed.
As mentioned above, by combining the conventional structure disclosed in Patent Document 2 and the conventional structure disclosed in Patent Document 3, forward displacement as well as upward displacement of the steering wheel in the event of a secondary collision can be suppressed. However, in addition to the problems mentioned above, problems in the conventional structure disclosed in Patent Documents 2 and 3 still remain, and the structure becomes highly complex. As a result, the cost inevitably becomes high.